In recent years, semiconductor integrated circuits have been increasingly microminiaturized and this makes pattern formation for the semiconductor integrated circuits more accurate in photolithography systems, for example. Meanwhile, as the order of the microminiaturization comes close to the wavelength of exposure light sources , the accuracy of the pattern formation has approached the limit. Therefore, electron beam lithography systems, a kind of charged particle beam systems, have been used for higher accuracy in place of the photolithography systems.
However, in pattern formation with the electron beam lithography system, an exposure time (drawing time) of patterns by an electron beam becomes longer as the number of the patterns increases, unlike pattern formation by a one-shot exposure process using an i-line or an excimer laser. Therefore, higher integration of semiconductor integrated circuits lengthens the time for the pattern formation and causes significant throughput degradation.
To enhance the speed of the pattern formation by electron beam lithography systems, cell projection lithography is being developed. In the cell projection lithography, masks in various shapes are combined and an electron beam is applied to them in a lump. However, this method also involves a problem that an Electron beam lithography system used in the cell projection lithography is large and requires an additional mechanism for controlling the mask positions with higher accuracy, increasing the cost of the systems.
As another pattern formation technique, an imprinting technique is known which presses a predetermined stamper to imprint its surface shape. With this imprinting technique, a stamper with relief structure on the surface corresponding to patterns to be formed is pressed against an object to be imprinted, which is made, for example, by forming a resin layer on a substrate. One stamper can be repeatedly pressed against plural pieces of the substrates to be imprinted having a microstructure with projections and depressions at an interval of 50 nm or less. This imprinting technique is considered to apply to formation of recording tracks and bit patterns in large-capacity recording media, for example. Substrates for the large-capacity recording media can be manufactured by etching a substrate using the projections of a pattern formation layer formed by the imprinting technique as a mask.
To form the recording tracks or the bit patterns of the large-capacity recording media, the accuracy of pattern imprinting is important. The imprinting techniques include a thermal imprinting in which thermoplastic resin is applied, and an optical imprinting in which photo-curing resin, which is cured when irradiated with ultraviolet light or the like, is applied. The thermal imprinting involves a heating and cooling process and the patterns goes out of shape owing to thermal expansion or shrinkage of the substrate or stamper. Therefore, the optical imprinting, free from a noticeable affect resulting from temperature change as the thermal imprinting, is suitable for formation of a microstructure of 50 nm or less.
The recording tracks and the bit patterns of the large-capacity recording media are formed on both surfaces of a substrate. Imprinting methods for this formation include a method of forming patterns on one surface at a time, and a method of forming patterns on both surfaces at a time. In the former method, imprinting can be carried out with a conventional system. But, during the imprinting, while one surface of an object to be imprinted is in contact with a stamper, the other surface is in contact with the pressing stage of the system, resulting in contamination of the other surface and loss of the patterns formed on the other surface. Consequently, it is desirable to clamp an object to be imprinted from both sides with stampers and press it as in the latter method.
To cure a photo-curing resin in the optical imprinting, the resin is required to be irradiated with light of a wavelength to which the photoinitiator in the resin reacts. The photo-curing resin is pressed between the stamper and the object to be imprinted. Therefore, if patterns are imprinted to only one surface of the object to be imprinted using a conventional imprinting device, either the stamper or the object to be imprinted should be composed of a transparent body and light is applied to the resin through this transparent body.
With a conventional imprinting device, light can be applied to both surfaces of an object to be imprinted if both the object to be imprinted and stampers are transparent. However, the substrate of the large-capacity recording media is opaque since it is composed of metal, such as aluminum, or has a metal multilayer film on the surface. Therefore, light cannot be applied to the opposite surface of an object to be imprinted to the light source.
To apply light to the opposite surface of the opaque object to be imprinted, a light application mechanism can be installed at the side of the opposite surface of the object to be imprinted. For example, JP-A-2007-026589 discloses a constitution that includes a parabolic reflector plate disposed at the opposite side of the object to be imprinted to the light source in order to reflect light from the light source to the opposite surface of the object to be imprinted. According to this invention, however, a part of a pressing stage, which disposed between the reflector plate and the object to be imprinted, becomes a blind and prevents the entire opposite surface from being irradiated with the light. Japanese Patent No. 3889386 discloses a constitution that includes a light application mechanism disposed at the same height as the surface of the object to be imprinted in order to apply light to the gap between the opaque object to be imprinted and the opaque stamper. However, the gap, which is several nm to several tens of nm, is so small that it is difficult to apply light to the whole surface of the object to be imprinted from the outer edge to the center.
As mentioned above, with a conventional imprinting device, when imprinting patterns on both surfaces of an opaque substrate at a time, it is substantially difficult to apply light to the opposite surface of an object to be imprinted to a light application mechanism.
It is an object of the present invention to provide an optical imprinting device capable of simultaneously imprinting fine patterns to both surfaces of an opaque substrate.